ansible.cfg: Fix remote_tmp

Newer versions of ansible no longer require a single top-level temporary
directory per user, as each run creates its own. Combined with the weird
random failures on *dc0.pyrocufflink.blue* that prevent Jenkins from
using Ansible occasionally, it's better to just let Ansible create its
own temporary directory directly in `/var/tmp` and clean up after itself
when it finishes.

ansible.cfg

@@ -7,4 +7,4 @@ gathering = smart
 fact_caching = jsonfile
 fact_caching_connection = .fact-cache
 
-remote_tmp = /var/tmp/.ansible-${USER}
+remote_tmp = /var/tmp